Basic of Computer Organisation
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Transcript of Basic of Computer Organisation
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Basic Computer Organization:
Microprocessor Organization -
Processor, Register, Clock
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4 main components:
1. Microprocessor
2. Memory
3. CPU Memory I/O Architecture
4. Instruction cycle
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Knowledge of these components and their
operation (interaction) offers insight into
system bottlenecks, alternate pathways,
magnitude of system failures, andopportunities for performance enhancement
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The functions performed by the CPU:
Fetch instructions
Fetch data
Process data
Write data
Organizational requirements that are derived fromthese functions:
ALU
Control logic
Registers
Internal CPU bus
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ALU: computation or processing of data (in
the internal CPU memory only)
Control logic: controls movement of data and
instructions into/out of the CPU; andcontrols the operation of ALU
Registers: internal temporary memory
Internal CPU bus: Means to move data and
instructions in and around the CPU
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Memory in the computer system can be
viewed in a hierarchy. (fig 3.3)
Memory in CPU: registers.
2 main roles of registers:
1. User-visible registers
2. Control and status registers
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To minimize usage of main memory, controlled bymachine or assembly-language program.
Can be categorized into 4 main categories: General purpose
Data
Address
Condition codes
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General purpose
Can be assigned a variety of functions
Ideally, they are defined orthogonally to the operationswithin the instructions
Data These registers only hold data
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Address
These registers only hold address information
Examples: general purpose address registers, segmentpointers, stack pointers, index registers
Condition codes Visible to the user but values set by the CPU as the result
of performing operations
Example code bits: zero, positive, overflow
Bit values are used as the basis for conditional jump
instructions
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General purpose registers maximize flexibility
in instruction design
Special purpose registers permit implicit
register specification in instructions reduces register field size in an instruction
No clear best design approach
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More registers permit more operands tobe held within the CPU -- reducingmemory bandwidth requirements to someextent
More registers cause an increase in thefield sizes needed to specify registers inan instruction word
Locality of reference may not support toomany registers
Most machines use 8-32 registers (doesnot include RISC machines)
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Address registers should be wide enoughto hold the longest address address!
Data registers should be wide enough to
hold most data types Would not want to use 64-bit registers ifthe vast majority of data operations used16 and 32-bit operands
Related to width of memory data bus Concatenate registers together to store
longer formats
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These registers are used during the fetching,
decoding and execution of instructions
Many are not visible to the user/programmer
Some are visible but can not be (easily)modified
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Program counter
Points to the next instruction to be executed
Instruction register Contains the instruction being executed
Memory address register A special register containing the address of a
word currently required
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Memory data/buffer register
Register of a computer's control unit thatcontains the contents of a register to fetch orstore from or to the computer storage.
Program status word(s) Superset of condition code register Interrupt masks, supervisory modes, etc. Status information
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